QUESTION:
Why does the message indicator remain displayed even though the counter is at zero?

ANSWER:  

Fig. 1: Message indicator (Meldeindikator) and counter (Zähler)

The message indicator indicates that there are alarm messages to be viewed or acknowledged. The message indicator is displayed whenever an alarm message arrives. 

The message indicator has two states:

• Flashing: as soon as at least one unacknowledged message is present.
• Static: when all alarm messages have been acknowledged, but at least one of them has not yet gone.

The counter:

• Counts up one for each alarm message that arrives
• Counts down one for each alarm message that goes
• Is zero when all the errors messages arrived have gone again.

The message indicator disappears when all alarm messages arrived have been acknowledged and gone again.

This property means that the message indicator with a counter state of "zero" can be displayed if a message has arrived, gone, but has not yet been acknowledged.

Keywords:
Message configuration, Message concept